There are various constraints in mobile stations used for a mobile communication system such as an INT 2000 system in that the mobile stations need to be small and lightweight, and to operate using a battery. Therefore, the mobile station in a standby state discontinuously performs operation for receiving signals from a base station to save power consumption (battery saving). More particularly, the discontinuous reception operation in the mobile station is performed under two stages.
FIG. 1 schematically shows a channel used for the discontinuous reception. In a first stage of the discontinuous reception operation, as shown in FIG. 1, the mobile station discontinuously receives PICH (Paging Indicator Channel). The cycle DRX for reception may be a value such as 640 ms, for example. The PICH periodically includes many paging indicators (PI) of a short period of 0.1 ms, for example. PIs are grouped into a plurality of groups, and they are indicated as P1, P2, . . . , Pq, . . . in FIG. 1. The mobile station discontinuously receives signals based on the timing of PI related to the own mobile station. PI indicates whether a paging signal addressed to the mobile station is occurring. The mobile station demodulates the PI, determines presence or absence of the paging signal addressed to the own station, and when it does not exist, the mobile station continues discontinuous signal reception of PI at next PI timing.
When there is the paging signal addressed to the own mobile station, the stage of the mobile station moves to a second stage of discontinuous reception. In the second stage, the mobile station receives the paging signal itself. The paging signal is transmitted using a transport channel PCH (Paging Channel) that is mapped to a physical channel SCCPCH (Secondary Common Control Physical Channel). The PCH is received over a relatively long period such as 10 ms, for example. The SCCPCH is associated with PICH such that time difference between them is τPICH. More particularly, the paging signal includes a paging request to the mobile station. The mobile station returns a paging response in response to the paging request, and after that, downlink data transmission starts. Conventional discontinuous reception method is described in the non-patent document 1, for example.
[non-patent document 1] Keiji Tachikawa (supervision), “W-CDMA mobile communication scheme”, MARUZEN, pp. 222-223